If you are frightened easily, stop reading this article immediately. But
if you want to learn about the fascinating way that wasps hunt
cockroaches, then this story is for you.

Many animals use toxins that target their
prey's nervous system. These neurotoxins usually work to paralyze the
prey. Researchers have found one animal, the predatory wasp, that uses
its venom not to paralyze, but to change the behavior of its
victim.

Scientists have known that predatory wasps sting cockroaches twice: the
first sting targets the thorax of the cockroach, the second sting targets
the head. The venom injected by the stings does not paralyze the
cockroach. Rather, after being stung, the cockroach cleans itself, then
slows down. The wasp then grabs an antennae of the cockroach and leads it
to a place where it can deposit its eggs. A few days later, the wasp's
offspring hatch and dine on the cockroach. Researchers have discovered
that the brain of the cockroach takes a direct hit by the second wasp
sting.

To identify the exact location of wasp stings, scientists at Ben-Gurion
University (Beer-Sheva, Israel) marked wasps by injecting them with
radioactive material. This injection labeled the wasp venom with
radioactivity. The wasps were then allowed to sting cockroaches.
Radioactivity was injected each time a wasp stung a cockroach.

When tissues of stung cockroaches were examined, the researchers found
that the brain of the cockroach had a higher level of radioactivity than
other parts of the body, including non-neural tissue in the head. To make
sure that the radioactive label did not spread from non-neural tissue to
the brain, the researchers in a separate experiment injected radioactive
material into areas around the brain. When these tissues were examined,
most of the radioactivity was located in non-neural tissue, not the brain.
From these data, the scientists concluded that the second wasp sting
targets the cockroach brain directly.

The researchers also measured the length of a wasp stinger. They found
that the stinger had a length of 2.5 mm. This is long enough to reach the
cockroach brain, which is located 1 to 2 mm deep in the head.

According to the scientists, this wasp-to-cockroach sting is the only
known example where a predator injects its venom directly into the central
nervous system of its prey. They speculate that the first sting into the
thorax of the cockroach helps the wasp target the brain more precisely.